When a distance between a main magnet attached to a rotor of a permanent-magnet electric motor and a rotating-position detection sensor provided on a stator is short, it is possible to detect a main magnetic flux generated from the main magnet for rotating the rotor. However, when the rotating-position detection sensor approaches a coil end of a winding part projected from the stator, the main magnetic flux of the main magnet is disturbed by the influence of a magnetic flux generated by a current flowing through the coil end. There is a case where position detection accuracy is deteriorated. Specifically, in a case where the motor is miniaturized, an influence of manufacturing error becomes large. Therefore, it is important to improve the position detection accuracy.
In a motor disclosed in Patent Literature 1, a main magnet and a position detection magnet are separated pieces. A rotating-position detection sensor is disposed apart from a stator coil, and the position detection magnet is disposed close to the rotating-position detection sensor. With this structure, the motor shown in Patent Literature 1 can eliminate the influence of a magnetic flux generated by the coil. Also, the main magnet and the position detection magnet are integrated with a rotor core so as to reduce variations in an assembling work.
A motor disclosed in Patent Literature 2 is configured so as to avoid the influence of a disturbance caused by a magnetism of a stator. To this end, the length in an axial direction of a permanent magnet forming a rotor is made longer than the length of the stator so that a part of the permanent magnet is extended in the axial direction from an action part of the stator, and a position detection sensor is provided in the extended part. With this structure, there is no need to provide a permanent magnet on a shaft for detection of the rotating position.
In a motor disclosed in Patent Literature 3, a rotor core includes two rotor cores, i.e., a first rotor core and a second rotor core which are obtained by dividing the rotor core in the axial direction of a rotor. A rare-earth magnet is inserted into the first rotor core, and a ferrite magnet is inserted into the second rotor core. Also, Patent Literature 3 discloses a structural example in which the second rotor core is disposed axially outside an end of a stator core.